FIG. 1 to FIG. 3B are schematic diagrams showing a prior art vertical contactor 100. FIG. 1 is a plan view of the contactor 100; FIG. 2 a cross sectional view showing the characterized structure of the contactor 100; FIG. 3A a cross sectional view showing the contactor 100 interposed between a semiconductor package P and a wiring plate 4 for the powered test of the package P; FIG. 3B a cross sectional view showing the contactor 100 to which an external pressure is applied to obtain a contact resistance required for the powered test.
The contactor 100 includes a multitude (several tens to several thousands) of contact springs 2 which are arranged in a matrix as shown in FIG. 1 and each of which is vertically oriented as shown in FIG. 2, a holder 6a for supporting the lower portions of these springs 2 and positioning them relative to the conductor members 4a of the wiring plate 4, and a floating guide plate 5 (referred to herein as a “guide plate”) for accepting and guiding the upper portions of the springs 2 and centering them relative to the contacts P2 of the back surface of the substrate P1 of the semiconductor package P.
As shown in FIG. 2, each of the contact springs 2 includes a long body portion 2c having a relatively large diameter, a neck portion 2a having a relatively small diameter and upwardly extending from the upper end of this body portion 2c, and a leg portion 2b downwardly extending from the lower end of the body portion 2c and tapered with a decreasing diameter to form a shoulder portion 2d from the body portion 2c to the neck portion 2a with a decreasing diameter and a seat portion 2e from the body portion 2c to the leg portion 2b with a decreasing diameter. The contact spring 2 is composed of a single conductive steel wire as twisted to have a “helical pitch larger than the diameter of the steel wire” in the intermediate portion of the body portion 2c (referred to herein as a “pitch helix”) except the upper and lower ends thereof in a normal condition (i.e., with no load), and a “helical pitch substantially equal to the diameter of the steel wire” in the rest (i.e., in the neck portion 2a, the upper and lower ends of the body portion 2c and the leg portion 2b which are referred to herein as a “tight helix”). In the tight helix, adjacent turns are contacting each other without a clearance to form a cylindrical conductor.
As shown in FIG. 2, the holder 6 includes an upper surface 6a and a bottom surface 6b in parallel with each other, and is formed with lower spring support holes 7 which are opened in the upper surface 6a and downwardly extending with a larger diameter than the spring body portion 2c and through holes 7d which are opened in the lower surface 6b with a smaller diameter than the spring body portion 2c and communicating with the lower spring support holes 7 to form steps 11 tapered with a decreasing diameter from the support hole 7 to the through holes 7d. 
When the contact spring 2 is inserted into the lower spring support hole 7, the spring 2 is stopped with the seat portion 2e being seated against the step 11 and supported in an upright attitude by the spring support hole 7 to project an upper half of the spring 2 from the holder upper surface 6a and the lower end of the leg portion 2b from the holder lower surface 6b. 
As shown in FIG. 2, the guide plate 5 also includes an upper surface 5a and a bottom surface 5b in parallel with each other, and is formed with upper spring support holes 9 which are opened in the lower surface 5b and upwardly extending with a larger diameter than the spring body portion 2c and guide holes 3 which are opened in the upper surface 5a with a smaller diameter than the spring body portion 2c, downwardly extending and communicating with the lower spring support holes 7 to form steps 8 tapered with a decreasing diameter from the support holes 9 to the guide holes 3.
This guide plate 5 has a rectangular profile as shown in FIG. 1.
When the upper half portions of the springs 2 projected from the holder upper surface 6a are engaged with the support hole 9 of the guide plate 5 followed by releasing the guide plate 5, the neck portions 2a are guided from the support hole 9 to the guide hole 3 and the steps 8 are seated against the shoulder portion 2d with the guide plate 5 moving downward. The guide plate 5 is then stopped with the springs 2 being compressed by a dimension corresponding to the own weight load L5 of the guide plate 5 per spring to obtain the distance d between the holder 6 and the plate 5 optimal for powered test. At this time, while the neck portion 2a of the spring 2 is located lower than the plate upper surface 5a, the upper end thereof is located in the upper half portion of the guide hole 3. If the total load applied to each spring 2 is Lt, Lt=L5 in the normal condition of the contactor 100 (FIG. 2).
The contactor 100 is provided for powered test in an assembled condition in which the wiring plate 4 is attached to the holder bottom surface (the condition as illustrated in FIG. 3A from which the package P is removed).
In this condition, the lower end of the leg portion 2b of the contact spring 2 is in line contact with the upper surface of the conductor member 4a flush with the upper surface of the wiring plate 4 closely contacting the holder bottom surface 6b to lift the seat portion 2e of the spring 2 from the step 11 of the holder 6 and lift the guide plate 5 increasing the distance d from the holder 6.
The powered test of the semiconductor package P is initiated by setting the package P on the assembly as illustrated in FIG. 3A. Namely, an electric contact P2 such as a hemispheric contact projected from the back surface of the substrate P1 of the package P is engaged with a guide hole 3 of the guide plate 5, and the back surface of the substrate P1 is seated against the plate upper surface 5a The neck portion 2 is centered in relation to the contact P2 by abutting the contact P2 against the upper end of the cylindrical and flexible neck portion 2a with its upper inner surface being in line contacts with the contact P2.
In this setting condition, the package load Lp per spring is exerted on each springs 2 which is thereby compressed to decrease the distance between the holder 6 and the guide plate 5 to d0. The total load Lt applied to each spring 2 is then Lt=L5+Lp.
In this case, since the guide plate 5 is supported by its steps 8 on the shoulder portions 2d of the springs 2, the depth of insertion of the neck portion 2a into the guide hole 3 is constant for each spring, and the degree of contact between the neck portion 2a and the corresponding contact P2 depends on the depth of insertion of the contact P2 into the guide hole 3. Because of this, the contact resistance between the neck portion 2a and the contact P2 slightly varies and becomes inequable in accordance with the location of the respective contact springs 2 as shown in FIG. 1 depending upon the ununiform surface contact between the back surface of the substrate P1 and the upper surface 5a of the guide plate 5 and the dispersion in manufacturing factors of the contact P2.
As shown in FIG. 3B, the powered test of the package P is conducted after uniformly contacting the back surface of the substrate P1 with the upper surface 5a of the guide plate 5 and uniformly applying an external force to the guide plate 5 in order to make the load on each spring equal to a predetermined value La At this time, the spring 2 is compressed in correspondence with the external force to decrease the distance between the holder 6 and the guide plate 5. The total load Lt applied to each spring 2 is then Lt=L5+Lp+La.